The present invention relates to a corrugating machine utilized in the manufacture of corrugated cardboards or paperboards and a corrugating roll design for use with the machine.
An example of a conventional xe2x80x9csingle facerxe2x80x9d corrugating machine for making a single faced corrugated cardboard is generally shown at 100 in FIG. 5. The single facer 100 generally comprises corrugating rolls consisting of a pair of upper and lower, counter-rotating, longitudinally toothed, corrugating rolls 110a and 110b for providing corrugations or flutes in a paper medium, or core A in a nip 160 created between the rolls 110a and 110b, a gluing section 120 for applying glue or adhesive to the tops of the flutes of the corrugated medium A as it is moved therepast, and a smooth surfaced pressure roll 130 disposed downstream of the gluing section for cooperating with the lower toothed roll 110b to bond the glued corrugated paper medium A and a paper liner B to each other to form a single faced corrugated cardboard product C. Each of the upper and lower corrugating rolls 110a and 110b has a tooth profile 140 defined by a plurality of tooth roots or bottom lands and a plurality of tooth tips extending longitudinally along the outer peripheral surface of the roll. Suction device 150 is disposed adjacent to the lower corrugating roll 110b to hold the corrugated medium A against the lower toothed roll 110b by suction.
In the conventional corrugating process using the single facer 100, a paper medium web is passed into the nip 160 formed by the inter-engaging teeth of the two corrugating rolls 110a and 110b, and this web begins to be deformed as it moves into an actual corrugating impression zone P in the nip where full engagement of the teeth takes place, i.e., one of the tooth tips of the upper roll 110a and the corresponding one of tooth roots of the lower roll 110b are in registration or in impression engagement. At the corrugating impression zone P, the medium web is formed into a final corrugated configuration as shown in FIG. 6. The corrugated medium A, after passing through the nip, is transferred to a glue applicator roll 170 of the gluing section 120 while being held by suction or vacuum against the lower corrugating roll 110b. Such transfer of the corrugated medium web can be accomplished by rotation of the lower corrugating roll 110b. The gluing section 120 picks up the glue contained in a glue reservoir 190 while rotating within the reservoir to be partially immersed in the glue therein, and applies the glue to the tops of the corrugations of the paper medium A. Doctor roll 180 is used to perform glue layer thickness control and provide for the application of a uniform glue layer to the tops of the corrugations of the medium A. The glued medium A is next passed between the lower corrugating roll 110b and the pressure roll 130 along with the liner B being carried around a portion of the pressure roll 130. The pressure roll 130 presses the glued corrugated medium A and the liner B against the lower corrugating roll 110b to bond the materials A and B to each other and thus produce a single faced corrugated cardboard paper product C.
The conventional design of the single facer 100 has the following disadvantages when used in the manufacture of the single faced corrugated cardboards.
Firstly, in order to ensure that the paper medium can be formed with the industrial standard type flutes and to prevent spring back of the fluted paper medium after it leaves the corrugating nip, it is required to provide a significant corrugating nip pressure between the pair of the corrugating rolls 110a and 110b at the corrugating impression zone P, the amount of which pressure is determined in accordance with a given center-to-center distance of the upper and lower corrugating rolls 110a and 110b. More specifically, the medium web can be clamped by the substantial corrugating nip pressure provided between one of the tooth tips 152 of the upper corrugating roll 110a and one of tooth roots 151 of the lower corrugating roll 110b, as shown in FIG. 7.
Paper tensile strength may depend mainly on frictional forces acting among the fibers of the paper medium and a degree of fiber entanglement. The fibers in the paper medium tend to be generally oriented in a direction perpendicular to the length of the roll as the paper medium moves through the corrugating nip. Application of substantial nip load to the medium at the corrugating nip position P may cause some of the fibers in the portion of the medium being corrugated to be cut, thereby resulting in a decrease of the degree of fiber entanglement. This may lead to a reduction strength or rupture of the corrugated paper medium and a decrease in the quality of the product.
Secondly, in order to handle a higher corrugating speed, the liner B is brought into contact with only the tops of the glued flutes of the paper medium A between the lower corrugating roll 110b and the pressure roll 130. In this case, the glue cannot fully penetrate into both of the medium A and the liner B. Thus, bonding may occur at interfaces between the liner B and the tops of the flutes of the medium A in which some of the fibers therein may be cut undesirably, thus resulting in reduction of the bonding strength and also reduction of the strength of the single faced corrugated cardboard product in the form of a trussed structure composed of the combined corrugated medium A and liner B.
To overcome the second disadvantage, Japanese Laid Open Patent Applicatio. No. 8-25531 proposes a pair of upper and lower corrugating rolls for a single facer wherein the corrugating rolls, instead of each having a tooth profile composed of a single arc, each have a profile of a tooth tip portion defined by a combination of a plurality of arcs that are symmetrical with respect to its center line. The tooth tip portion of each of the corrugating roll has a gentle arc form that has no abrupt change in curvature. With this arrangement, a substantially uniform distribution of contact pressure exerted on the liner and paper medium webs can be accomplished as they are compressed between the pressure roll and the lower corrugating roll.
As can be appreciated, however, the pressure roll has a smooth cylindrical surface whereas the lower and upper corrugating rolls have their tooth profiles. Accordingly, application of the teachings of the 8-25531 application to the pair of upper and lower corrugating rolls defining the corrugating nip therebetween would not prevent the loss of the strength of the paper corrugated medium because of the cut fibers mentioned above with regard to said second disadvantage. Moreover, modification of the corrugating roll design having the tooth profile composed of a single arc into that having the tooth profile defined by the combination of the plurality of arcs mentioned above may require delicate machining operations.
Also, for overcoming the problem as described in connection with the high corrugating speed, Japanese Laid Open Patent Application No. 6-23884 discloses a single facer machine wherein a liner web can be bond to a corrugated paper medium web under a reduced contact pressure in a nip formed by lower corrugating and pressure rolls. In the single facer of the 6-23884 application, the liner contacts the glued flute tips of the corrugated medium in the pressure nip formed by the pressure roll and the lower corrugating roll, with the liner web being tensioned by means of tensioning rolls disposed upstream and downstream of the lower corrugating roll in order to reduce the substantial contact pressure which would be otherwise required at the pressure nip.
However, it is not practical to apply the teachings of the 6-23884 application to the pair of upper and lower corrugating rolls defining the corrugating nip because high corrugating nip pressure is required at the nip defined between the upper and lower corrugating rolls whereas relatively low contact pressure is applied at the pressure nip between the lower corrugating roll and the pressure roll so as to provide an initial bond between the corrugated paper medium and the liner webs.
In practice, it is difficult to apply the teachings of the 6-23884 application to the upper pair of and lower corrugating rolls.
In view of the above-mentioned problem encountered with a corrugating nip formed by upper and lower corrugating rolls, it is an object of the invention to provide a corrugation roll design for a corrugating machine which prevents failure of the fibers in a paper medium web when it is corrugated, thereby maintaining the required strength of the paper medium.
Also, in view of the above-mentioned problem encountered with a pressure nip formed by lower corrugating and pressure rolls, it is another object of the invention to provide a corrugating machine wherein a paper liner web is combined with glued flute tops of the paper medium in which the fibers therein are not cut, thereby preventing, loss of strength of the corrugated cardboard.
Furthermore, it is another object of the invention to cost-effectively modify or retrofit the existing corrugating rolls in a manner so as to prevent the loss of the strength of the corrugated cardboard.
In order to attain these and other objects, the present invention provides a corrugating roll design for a corrugating machine comprising a pair of parallel, spaced apart, corrugating rolls which rotate in opposite directions on their respective rotational axes, the rotational axes of the corrugating rolls being spaced apart a predetermined distance, and each of the corrugating rolls being formed along its outer peripheral surface with longitudinally extending teeth with tooth tips and tooth roots, a paper medium to be corrugated adapted to be fed into a nip formed by the teeth of the corrugating rolls inter-engaging, and begin to be deformed as it moves into an actual corrugating impression zone in the nip where full engagement of the teeth takes place, thereby providing corrugations in the paper medium, characterized by depressions provided in the tops of the tooth tips of at least one of the corrugating rolls and spaced apart a predetermined distance along the length of the roll, each of said depressions having a bottom surface which is located to establish a spacing between the bottom surface of the depression and the tooth root of the other corrugating roll at the actual corrugation impression zone in the nip, the above mentioned spacing being greater than the thickness of the medium.
According to one feature of the invention, the ratio of the sum total of the axial lengths of the depressions to the transverse dimension of the paper medium measured longitudinally of the above mentioned at least one of the corrugating roll is greater than a predetermined value.
Preferably, the bottom surface of each of the depressions is of a generally convex arc configuration in a direction toward the other corrugating roll with a radius of curvature greater than that of the tooth tips of said at least one of the corrugating rolls in a plane generally perpendicular to the longitudinal direction of the roll.
According to another feature of the invention, each of the depressions can be provided at its opposite sides with ramps extending in a divergent fashion from the bottom surface thereof to the top of the tooth tip of the above mentioned at least one of the corrugating rolls.
It is preferable for each of the tooth profiles of the corrugating rolls to be comprised of a combination of a plurality of arcs that are symmetrical with respect to a center line of the tooth tip, i.e., a line connecting the apex of the tooth tip and the rotational axis of the corrugating roll.
According to another feature of the invention, the depressions of adjacent teeth or tooth tips of the above mentioned at least one of the corrugating rolls are offset from one another along the length of the corrugating roll.
Preferably, the depressions are disposed in a helical pattern along the peripheral surface of the corrugating roll.
The present invention also provides a corrugating machine comprising the pair of corrugating rolls as defined above, the corrugating rolls cooperating to provide a corrugated paper medium, gluing means for applying glue to the flute tops of the corrugated medium, and pressure means disposed downstream of the gluing means for cooperating with one of the corrugating rolls to compress the corrugated medium and a liner therebetween to bond them.
The present invention also provides a double facer comprising a pair of parallel, spaced apart, corrugating rolls which rotate in opposite directions on their respective rotational axes, the rotational axes of the corrugating rolls being spaced apart a predetermined distance, and each of the corrugating rolls being formed along its outer peripheral surface with longitudinally extending teeth with tooth tips and tooth roots, a paper medium to be corrugated adapted to be fed into a nip formed by the teeth of the corrugating rolls inter-engaging, and begin to be deformed as it moves into an actual corrugating impression zone in the nip where full engagement of the teeth takes place, thereby providing corrugations in the medium, each of said corrugating rolls having depressions provided in the tops of the tooth tips thereof and spaced apart a predetermined distance along the length of the roll, each of the depressions having a bottom surface which is located to establish a spacing between the bottom surface of the depression and the tooth root of the other corrugating roll at the actual corrugation impression zone in the nip, the above mentioned spacing being greater than the thickness of the paper medium; first gluing means for applying glue to the flute tops of one of faces of the corrugated medium; first pressure means disposed downstream of the first gluing means for cooperating with the one of the corrugating rolls to compress the glued flute tops of the one face of the corrugated paper medium and a first liner therebetween to bond them; second gluing means disposed downstream of the first pressure means for applying glue or adhesive to the flute tops of the other face of the paper medium; and bonding means disposed downstream of the second gluing means for bonding a second liner web to the glued flute tops of the other face of the corrugated medium.
In an operation of the corrugating rolls according to the invention, a paper medium web is fed into the nip between the inter-engaging teeth of the upper and lower corrugating rolls rotating in opposite directions. The medium web begins to be deformed or folded as it moves into the corrugating impression zone in the nip where it is formed with corrugations or flutes.
More specifically, the upper and lower corrugating rolls are disposed parallel to each other at a predetermined center-to-center spacing. At the impression zone, the paper medium web is clamped or pinched between one of the tooth tips of one of the corrugating rolls and one of the tooth roots of the other corrugating roll at the impression zone under a predetermined nip load and thus is formed into its final fluted or corrugated configuration without any spring back occurring.
In view of that fact that depressions are provided in the tops of the tooth tips of at least one of the corrugating rolls and spaced apart a predetermined distance along the length of the roll, at the corrugating impression zone, some areas where the paper medium web is sandwiched between one of the tooth tips of one of the corrugating rolls and one of the tooth roots of the other corrugating roll as well as other areas where the paper medium web is sandwiched between the depressions on one of the tooth tips of one of the corrugating rolls and one of the tooth roots of the other corrugating roll are scattered along the length of the roll.
Since, as has already been stated, each depression of one of the corrugating rolls has a bottom surface which is located to establish a spacing between the bottom surface of the depression and one of the tooth roots of the other corrugating roll at the impression zone, substantially no corrugating nip pressure is exerted on the paper medium at said some areas, thereby preventing failure of the fibers in the paper medium web while at the same time, sufficient corrugating nip load is imposed on the paper medium web at said other areas.
The corrugated cardboard making machine having the corrugating rolls constructed in accordance with the invention prevents failure or cutting of the fibers in the paper medium during corrugating impression. As a result, the required strength of the medium web can be maintained. In addition, since the liner is combined with the glued paper medium in which the fibers remain intact by pressure means through the bonding of the surface of the liner with that of the paper medium, the required strength of the finished corrugated cardboard can be maintained.